Listening for key events

I have a 3-D surface that represents the number of documents associated
with a particular word stem.  A green blob hovers just above the
surface and represents a stem of interest.  I would like the blob to
hover just above the highest peak and move to the next highest when the
tab key is pressed.  If shift-tab is pressed the blob moves to next
higher peak.  This is illustrated at

the Java source is at

My question is, how can I intercept tab/shift-tab key presses when the
graph has focus so I can in-turn move the green blob?  I tried adding a
KeyListener without any luck.  I also checked out the VisAD examples
and did not see any that react to key presses.

Thanks in advance for any help.